Many developing technologies have been embraced because they increase accessibility to information. Examples of such technologies include microfilm, magnetic tapes, magnetic disk media, optical disk media, and integrated memories. Integrated memories in particular offer a high degree of accessibility.
Integrated memories are electrical circuits that are configured to store information in digital form. This information, or “data,” is readily accessible to any digital device appropriately coupled to the integrated memory. Depending on the particular technology employed, data can be accessed at truly astonishing rates.
Integrated memories are often classified as volatile or non-volatile. Volatile integrated memories suffer loss of stored data in the absence of electrical power, but this shortcoming may be offset by advantages in information density and access rates. Non-volatile memories retain their stored information in the absence of electrical power, but may suffer from a reduced information density, a reduced access rate, and/or a lack of programmability.
Magnetic random access memory (MRAM) offers programmability, non-volatility, high information density, and a moderate access rate. MRAMs, as that term is used herein, are integrated memories that use magnetic fields to store data. These magnetic fields can be embedded in magnetic materials that do not rely on the continued presence of electrical power to preserve the magnetic fields. A variety of sensing techniques may be employed to detect magnetic fields in these memories and to determine the data these fields represent.
In one type of MRAM, data is stored in an array of memory elements. Each of the memory elements may include two magnetic layers separated by an insulating layer. The magnetic orientations of the two layers may be aligned (“parallel”) or opposed (“anti-parallel”). These parallel and anti-parallel conditions may cause the memory element to have different electrical resistances. The two resistance values may be associated with digital values (e.g., 0 and 1), allowing each memory element to store one binary digit (“bit”) of information. The stored bit may be detected by measuring the resistance of the memory element, e.g., by measuring an electrical voltage or current when electrical energy is supplied to the memory element.
As part of the manufacturing process, variations may develop within an array of memory elements. Consequently, different memory elements may have different resistances when they represent a given digital value. The variation may be enough to prevent the use of a standard threshold value to distinguish between digital values. For example, if in each memory element the resistance associated with a digital 0 is higher than the resistance associated with a digital 1, any processing variation that significantly increases the resistance of some of the memory elements may cause their digital l's to be mistaken for O's when a low threshold value is used. Conversely, if a higher threshold value is used, the digital 0's in the other memory cells may be mistaken for 1's. The presence of electrical noise in the integrated memory will only exacerbate this problem.
Thus, improved methods for detecting data stored in MRAM cells are desirable.